This invention relates to a sensor for indicating orientation of a satellite on which the sensor is mounted, and more particularly, to an earth/star sensor which measures Yaw as well as Pitch and Roll.
Horizon sensors are devices which are mounted in satellites, space probes and the like, which sense the horizon of the earth, and produce a signal which indicates orientation of the satellite with the respect to the earth being orbited. Almost all unmanned satellites employ horizon sensors for attitude control and guidance of the satellite. The attitude of the satellite is determined by its position with respect to three axes at right angles to each other. Two of these axes are in a plane at right angles to a projected radius of the earth passing through the satellite which are known as Pitch and Roll, and the third coincides with such a radius known as Yaw. Once the Pitch and Roll of the satellite are determined, orientation around the Yaw axis is usually determined by other means, such as a gyroscope, or the observation of other heavenly bodies. The problem in providing various attitude information, including Yaw, normally requires additional equipment in the form of a plurality or different sensor heads. This is costly, requires increased power, and adds weight to the spacecraft, all of which are undesirable.